The oxygen sensor is usually located on the gathering area of the exhaust manifolds. All exhaust gas leaving the engine flows past the oxygen sensor. The oxygen sensor produces an electrical voltage when exposed to oxygen present in the exhaust gases. Where there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage. When there is a lesser amount of oxygen present (rich mixture), the sensor produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich/lean switch. The voltage from the sensor is transmitted to the Engine Control Unit (ECU), which changes the fuel injection ratio accordingly. On later models, the oxygen sensor may be electrically heated internally. This allows for faster switching during cold engine operation.
| Fig. 1: Oxygen sensor location — 1.8L
engines
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| Fig. 2: Early 2.0L engines were equipped with a non-heated
oxygen sensor. Later models utilized a heated one
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